1. Field of the Invention
This invention relates to an electrode for a coulometric type of electrochemical detector capable of providing a highly sensitive detection of trace amounts of electrically active substances isolated by, for example, liquid chromatography, a process for preparing it and an analytical apparatus in which it is built.
2. Background Art
Heretofore, electrochemical detectors having electrodes designed therefor have been used for the detection and determination of trace amounts of electrochemically active substances contained in biopsy such as catecholamines and their metabolites because they can be used in combination with liquid chromatography to enable the highly sensitive detection of such substances.
Amperometric types of electrodes have so far been used as such electrodes for electrochemical detectors, but it has been found that they cannot be applied to more precise analysis because of their limited resolving power. Known as the electrode capable of enabling detection to the highest sensitivity is one used with a coulometric type of electrochemical detector.
Essentially required for such an electrode for the coulometric type of electrochemical detector is that:
(1) it should be formed of an electrically conductive material having a high surface area sufficient for efficient reactions, because it is desired that the substances to be detected pass through an electrode cell while they are all electrochemically converted;
(2) its surface should have a low polarity and be chemically stable since it is required to possess durability over an extended period of time; and
(3) it should have a uniform pore diameter distribution so as to prevent clogging in electrode cells.
As electrically conductive materials which can meet such conditions (1), (2) and (3), it is preferred to use carbonaceous substances, inter alia, those in the form of graphite that is of low polarity and chemically stable, as known from U.S. Pat. No. 4804455.
However, such graphite-form carbonaceous substances as set forth in U.S. Pat. No. 4804455 are so small in their surface area and so poor in their mechanical stability that they place some limitation upon being used as materials for electrodes for the coulometric type of electrochemical detectors in particular.